1. Field of the Invention
The present invention relates to a combination MR (magnetoresistive)/inductive thin film magnetic head carried on, for example, a hard disk drive, and particularly to a thin film magnetic head in which materials of an upper core layer and a lower core layer are improved to improve magnetic characteristics, and a manufacturing method thereof.
2. Description of the Related Art
FIG. 15 is an enlarged sectional view showing a conventional thin film magnetic head as viewed from the side thereof opposite to a recording medium.
This thin film magnetic head comprises a reading head h1 which employs the magnetoresistive effect and a writing inductive head h2, which are laminated on the trailing-side end surface of a slider which constitutes, for example, a floating head.
The reading head h1 comprises a lower shielding layer 1 made of sendust, an Ni--Fe alloy (permalloy) or the like, a lower gap layer 2 made of a non-magnetic material such as Al.sub.2 O.sub.3 (aluminum oxide) or the like and formed on the lower shielding layer 1, and a magnetoresistive element 3 deposited on the lower gap layer 2. The magnetoresistive element 3 comprises three layers including a soft adjacent layer (SAL), a non-magnetic layer (SHUNT layer), and a magnetoresistive layer (MR layer) which are laminated in turn. Generally, the magnetoresistive layer comprises an Ni--Fe alloy (permalloy) layer, the non-magnetic layer comprises a tantalum layer, and the soft adjacent layer comprises an Ni--Fe--Nb alloy layer.
On both sides of the magnetoresistive layer 3 are formed hard bias layers serving as longitudinal bias layers. On the hard bias layers are formed main lead layers 5 made of a non-magnetic conductive material having low electric resistance, such as Cu (copper), W (tungsten) or the like. On the main lead layers 5 is further formed an upper gap layer 6 made of a non-magnetic material such as aluminum oxide or the like.
On the upper gap layer 6 is formed a lower core layer 20 by plating permalloy. In the inductive head h2, the lower core layer 20 functions as a leading-side core portion which gives a recording magnetic field to a recording medium. In the reading head h1, the lower core layer 20 functions as an upper shielding layer, and a gap length G11 is determined by the gap between the lower shielding layer 1 and the lower core layer 20.
On the lower core layer 20 are laminated a gap layer (non-magnetic material layer) 8 made of aluminum oxide or the like, and an insulation layer (not shown in the drawing) made of polyimide or a resist material, and a coil layer 9 patterned to a spiral form is provided on the insulation layer. The coil layer 9 is made of a non-magnetic conductive material having low electric resistance, such as Cu (copper) or the like. The coil layer 9 is surrounded by an insulation layer (not shown) made of polyimide or a resist material, and an upper core layer 21 made of a magnetic material such as permalloy is formed on the insulation layer by plating. The upper core layer 21 functions as the trailing-side core portion of the inductive head h2 which gives a recording magnetic field to the recording medium.
As shown in FIG. 15, on the side opposite to the recording medium, the tip 21a of the upper core layer 21 is opposed to the upper side of the lower core layer 20 with the gap layer 8 therebetween to form a magnetic gap having a magnetic gap length G12 which gives a magnetic field to the recording medium. On the upper core layer 21 is provided a protective layer 11 made of aluminum oxide or the like.
In the inductive head h2, when a recording current is supplied to the coil layer 9, a recording magnetic field is applied to the upper core layer 21 and the lower core layer 20 from the coil layer 9. In the magnetic gap, magnetic signals are recorded on the recording medium such as a hard disk by a leakage magnetic field between the lower core layer 20 and the upper core layer 21.
FIG. 16 is an enlarged sectional view showing a conventional method of producing the lower core layer 20.
As shown in FIG. 16A, a base layer 22 made of a magnetic material such as permalloy or the like is formed on the upper gap layer 6 by plating. On the base layer 22 is coated a resist solution, followed by exposure to form rectangular resist layers 23 on the base layer 22. In FIG. 16B, magnetic material layers 20 and 24 made of permalloy or the like are formed, by plating, on portions of the base layer 22 where the resist layers 23 are not formed. The magnetic material layer 20 formed between the resist layers 23 is left behind as the lower core layer.
In FIG. 16C, the resist layers 23 are removed, and portions of the base layer 22 which are formed below the resist layers 23 are removed by ion milling. In FIG. 16D, a protective layer 25 made of a resist material is formed on the portions on the upper gap layer 6 where the resist layers 23 were removed, to cover the magnetic material layer 20. In FIG. 16E, the magnetic material layers 24 and portions of the base layer 22 which are formed directly below the magnetic material layers 24 are removed by wet etching. In FIG. 16F, the protective layer 25 is removed to leave only the rectangular lower core layer 20 on the upper gap layer 6 with the base layer 22 therebetween.
The conventional thin film magnetic head shown in FIG. 15 comprises the lower core layer 20 formed by plating permalloy and thus has the following problems.
(i) Since the lower core layer 20 (the upper shielding layer) is thick and has a substantially rectangular sectional shape, step portions A each having a corner are formed at both side ends of the lower core layer 20. Therefore, it is difficult to form the gap layer 8 having a uniform thickness on the lower core layer 20. Particularly, the thickness of the gap layer 8 is extremely small near the corners of the step portions A at both side ends of the lower core layer 20, and thus an insulation failure easily occurs between the lower core layer 20 and the coil layer 9.
Also, in order to increase the recording density, it is necessary to thin the gap layer 8 to decrease the gap length G12 of the magnetic gap. However, when the gap layer is thinned, pin holes easily occur in the gap layer 8 near the step portions A.
(ii) Since the lower core layer 20 (the upper shielding layer) has a rectangular sectional shape, and the step portions A are formed at both side ends thereof, a difference in height is also formed in the surface of the gap layer 8 formed on the step portions A. Therefore, when the area of the lower core layer 20 is smaller than the region of the coil layer 9, the coil layer 9 is formed on the step portions of the gap layer 8, thereby making it difficult to form the coil layer 9 and easily causing defects in the coil layer 9.
(iii) In order to increase the recording density of signals on the recording medium, and increase the magnetic writing frequency, it is necessary to improve the soft magnetic characteristics of the lower core layer 20 and the upper core layer 21 to impart low coercive force and high resistivity thereto. Although the saturation magnetic flux density is preferably as high as possible, particularly when the saturation magnetic flux density of the lower core layer 20 is lower than that of the upper core layer 21 so that magnetization of a leakage magnetic field between the lower core layer 20 and the upper core layer 21 is easily reversed, the density of signal writing on the recording medium can possibly be increased.
In the thin film magnetic head shown in FIG. 15, since the lower core layer 20 functions not only as a leading-side core portion for the inductive head h2 but also as an upper shielding layer for the reading head h1, the lower core layer 20 must be provided with both the properties as a core and the properties as a shield.
In order to improve the shielding function of the lower core layer 20, the direction (the direction perpendicular to the drawing of FIG. 15) of an external magnetic field applied from the recording medium is preferably the direction of the hard axis of magnetization, the saturation magnetic flux density is not excessively high, and the lower core layer 20 preferably has low coercive force and a low magnetostriction constant in order to prevent excessive increase in the saturation magnetic flux density.
Also, in order to further increase the density of signal recording on the recording medium, it is necessary to improve the soft magnetic characteristics of the lower core layer 20 and the upper core layer 21, and decrease the gap length G12 of the magnetic gap in the inductive head h2. Therefore, the non-magnetic material layer 8 is formed to be as thin as possible.
Further, in the reading head h1, in order to improve the resolution of the leakage magnetic field from the recording medium subjected to high-density recording, it is necessary to decrease the gap length G11 of the magnetic gap. Therefore, the lower gap layer 2 and the upper gap layer 6 are formed to be as thin as possible.
However, even if the magnetic gap is decreased, when the shielding function of the lower core layer 20 deteriorates, the MR layer of the magnetoresistive element layer 3 cannot be shielded from recording noise of the recording medium and thus captures excess signals, thereby causing the problem of easily producing Barkhausen noise.
As described above, the lower core layer 20 having both the leading-side core function for the inductive head h2 and the upper shielding function for the reading head h1 is preferably made of a soft magnetic material having a lower saturation magnetic flux density than the upper core layer 21, low coercive force, high resistivity and a low magnetostriction constant.
However, permalloy which forms the conventional lower core layer 20 and upper core layer 21 has a relatively high saturation magnetic flux density of 1.0 T (tesla) and coercive force of as low as 0.5 Oe (oersted) in the direction of hard axis, but has a resistivity of as low as 30 (.mu..OMEGA..cm). Therefore, when the recording frequency is further increased, an eddy current occurs in the lower core layer 20 and the upper core layer 21, and thus a heat loss due to the eddy current is increased. Also the magnetic permeability in a high frequency region deteriorates, thereby deteriorating the shielding function and easily producing Barkhausen noise in the MR layer.
U.S. Pat. No. 5,573,863 discloses s soft magnetic material comprising a mixture of a bcc-structure Fe fine crystalline phase and an amorphous phase containing an element selected from the rare earth elements, Ti, Zr, Hf, V, Nb, Ta and W, and 0. The composition ratios of the soft magnetic material can be appropriately adjusted to obtain a high saturation magnetic flux density, low coercive force and high resistivity. Therefore, the use of the soft magnetic material for the lower core layer 20 and the upper core layer 21 enables manufacture of a thin film magnetic head having excellent magnetic characteristics.
With this soft magnetic material, a film cannot be formed by plating, but can be formed only by a sputtering method or an evaporation method. However, a conventional method of manufacturing a thin film magnetic head is difficult to form the lower core layer 20 by the sputtering method or evaporation method. The reasons for this will be described below.
When the lower core layer 20 is formed by the sputtering method, a layer of the soft magnetic material is formed directly on the upper gap layer 6 made of aluminum oxide or the like. However, in order to form the soft magnetic material layer in a predetermined shape, unnecessary portions must be removed by ion milling (dry etching). However, ion milling for removing the soft magnetic material layer causes the problem of damaging the upper gap layer 6 made of aluminum oxide formed below the soft magnetic material layer.
Although the upper gap layer is formed to a thickness of about 1000 angstroms, the lower core layer is formed to a larger thickness than the upper gap layer. It is generally thought that ion milling for removing a predetermined thickness causes a tolerance of about 5% for a thickness which can be removed. Therefore, ion milling for removing a predetermined portion of the lower core layer makes the thin upper gap layer formed below the lower core layer easy to damage due to the tolerance of about 5% for the thickness removed.
For the above described reasons, the lower core layer 20 is removed by ion milling, and at the same time, the upper gap layer 6 is partly removed. In the worst case, the entire upper gap layer 6 is removed, and thus the main lead layer 5 formed below the upper gap layer 6 is affected by ion milling.